1. Field of the Invention
The invention relates to a method for improving optical measurement of gas concentration.
2. Description of Background Art
In U.S. Pat. No. 5,527,031 is described an optical measurement method where a reference gas cell is used for the calibration and locking of the device on an oxygen absorption line. This method is rather complicated and is susceptible to changes in the measurement environment. WO 87/07018 describes a calibration method in connection with a oxygen concentration measurement device. In this method the wavelength of the emitting laser is scanned through a range of wavelengths that includes the absorption line.
U.S. Pat. No. 6,269,110 describes a calibration method for tunable ArF-excimer laser. In this solution the laser has a discharge chamber where a molecular species is introduced for calibration purposes.
U.S. Pat. No. 6,107,631 describes a self-calibration approach for tunable laser spectral absorption sensors. In this solution stored calibration information is used with current sensor reading information for calibration purposes.